The present invention relates to gathering machines for use in bookbinding and analogous plants wherein discrete (folded or unfolded) sheets or groups of sheets (e.g., signatures) are assembled to form stacks of dissimilar sheets or dissimilar groups of sheets. More particularly, the invention relates to gathering machines of the type wherein a conveyor transports partly grown stacks of sheets past several magazines for piles of identical sheets and wherein the sheets which are withdrawn from successive magazines are stacked on top of each other. Still more particularly, the invention relates to gathering machines of the type wherein sheets which are withdrawn from magazines are deposited on platforms or analogous supports prior to stacking of such sheets on top of each other to constitute brochures, pamphlets, books, newspapers or analogous commodities. As a rule, the sheets which descend onto or are otherwise deposited on the platforms are removed by pushers or analogous entraining elements of the conveyor which is driven to advance the pushers along a horizontal path below the platforms.
A drawback of the just described gathering machines is that the pushers effect an abrupt removal of sheets from the respective platforms. This can result in pronounced deformation of and/or other damage to sheets, especially if the sheets are readily flexible and/or if the gathering machine is intended or designed to accumulate a large number of stacks of dissimilar sheets or dissimilar groups of sheets per unit of time. In fact, abrupt acceleration of sheets (especially discrete sheets) from zero speed to the full speed of pushers is even likely to entail deformation of and/or other damage to relatively stiff sheets. Excessive deformation, tearing and/or other damage to sheets and/or groups of sheets greatly affects the output of a gathering machine because the machine must be decelerated or arrested without delay at frequent intervals in order to allow for removal of defective sheets, groups of sheets and/or partly grown or fully grown stacks without risking injury to attendants and/or damage to component parts of the machine. Therefore, the maximum output of the just described gathering machines is relatively low because the speed of the pushers cannot exceed a rather low value in order to reduce the likelihood of deformation of sheets during transfer from the respective platforms.
Swiss Pat. No. 425,721 a modified gathering machine wherein the platforms are movable in and counter to the direction of advancement of pushers so as to accelerate the freshly deposited sheets during forward movement and prior to entrainment of such sheets by the oncoming pushers. The patent proposes to accelerate the sheets at least close to the speed of the oncoming pushers prior to stripping of such sheets off the corresponding platforms. The patented machine is less likely to damage the sheets; however, the platforms must be reciprocated at a high frequency and their mass is relatively high so that the machine which embodies such structure must employ a bulky and sturdy frame which is securely anchored to the floor. The wear upon the platforms, and especially upon the means for reciprocating the platforms, is very pronounced, particularly if the patented machine is to turn out a large number of fully grown stacks per unit of time.